ALSA: usb-audio: Add dB range mapping for Sennheiser Communications Headset PC 8

commit ab2165e2e6ed17345ffa8ee88ca764e8788ebcd7 upstream.

The decibel volume range contains a negative maximum value resulting in
pipewire complaining about the device and effectivly having no sound
output. The wrong values also resulted in the headset sounding muted
already at a mixer level of about ~25%.

PipeWire BugLink: https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/1049

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=212897
Signed-off-by: Timo Gurr <timo.gurr@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210503110822.10222-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

sound/usb/mixer_maps.c

@@ -337,6 +337,13 @@ static const struct usbmix_name_map bose_companion5_map[] = {
 	{ 0 }	/* terminator */
 };
 
+/* Sennheiser Communications Headset [PC 8], the dB value is reported as -6 negative maximum  */
+static const struct usbmix_dB_map sennheiser_pc8_dB = {-9500, 0};
+static const struct usbmix_name_map sennheiser_pc8_map[] = {
+	{ 9, NULL, .dB = &sennheiser_pc8_dB },
+	{ 0 }   /* terminator */
+};
+
 /*
  * Dell usb dock with ALC4020 codec had a firmware problem where it got
  * screwed up when zero volume is passed; just skip it as a workaround
@@ -619,5 +626,10 @@ static const struct usbmix_ctl_map uac3_badd_usbmix_ctl_maps[] = {
 		.id = UAC3_FUNCTION_SUBCLASS_SPEAKERPHONE,
 		.map = uac3_badd_speakerphone_map,
 	},
+	{
+		/* Sennheiser Communications Headset [PC 8] */
+		.id = USB_ID(0x1395, 0x0025),
+		.map = sennheiser_pc8_map,
+	},
 	{ 0 } /* terminator */
 };